Gas tank out, sub box in?

[71ChevySS(straight6)]

I just thought about something else: what if the sub was firing down? How wide is the bottom of you guys's boxes? could a twelve fire down with no issues? K10, wish I could go to a console and buckets, but I have to haul three people sometimes, so I need that bench. I believe it's the 2nd row bench out of a '92 Suburban. I'm not positive, but I think that's what my dad said he put in there to replace the stock seats. Does that help anybody? Thanks!